The invention concerns an arrangement for driving a discharge spout of an agricultural harvesting machine, and more specifically, concerns a drive including a motor, that is connected with the discharge spout over a driveline, and is arranged to pivot the spout about an approximately vertical axis, where an overload clutch is inserted into the driveline that interrupts the driveline when a threshold value of the torque transmitted to the discharge spout is exceeded.
In harvesting machines with discharge spouts that can be rotated about a vertical axis, such as combines with ejection ducts and forage harvesters with curved ejection ducts, there is the danger that the discharge spout can be damaged if it is thrown against an obstacle, such as a tree standing at the edge of the field, a power line pole or a transport vehicle operating alongside.
EP 0 492 195 A proposes that the drive arrangement including a worm gear meshed with a turning circle of a curved discharge duct of a forage harvester will automatically disengage when excessive torques are applied to the discharge duct. Thereby the curved discharge duct can rotate freely and avoid an obstacle. The worm gear is blocked in the disengaged position by a blocking pawl. Therefore an operator must again release the blocking pawl after the trouble has been removed. The operator must therefore climb out of the operator""s cab in order to release the blocking pawl at a location that is difficult to access and can continue the operation only after that. The free rotation of the curved discharge duct after the worm gear has been disengaged also has its problems, because after a first impact with an obstacle it can then recoil and collide with another obstacle and be damaged thereby.
EP 0 672 339 A proposes that a shear pin be inserted into the driveline of the curved discharge duct of a forage harvester which shears upon unusual loading of the curved discharge duct. After the end of the unusual overload the shear pin must be replaced since it is usually located in a relatively inaccessible location this is possible only with a considerable time delay. If no shear pin is available the forage harvester cannot be used for an extended period of time. Furthermore the aforementioned disadvantages of the ability to rotate freely still remains.
EP 1 092 342 A discloses a forage harvester whose curved discharge duct can be moved by a hydraulic motor. A pressure relief valve and feeder valve are arranged between the supply line and/or the return line of the hydraulic motor and the oil leakage line. The result is that in the case of a collision the hydraulic motor acts as a pump and brakes the curved discharge duct with a specified force. If it is driven for repositioning of the curved discharge duct just at the point of impact, the oil pressure that drives it is bled off by the pressure relief valve. The disadvantage here is that the hydraulic motor provides a relatively high braking effect on the basis of the gear ratio of the intervening gearbox, so that damage to the curved discharge duct remains conceivable. This solution is also relatively expensive and costly due to the necessary hydraulic elements.
The problem underlying the invention is seen in the need to define an arrangement that is not too costly for the drive of a discharge spout that avoids damage to the discharge spout in the case of an impact of the discharge spout with an obstacle and that is distinguished by operator friendliness.
According to the present invention, there is provided an improved drive for repositioning the discharge duct or spout of an agricultural harvester.
An object of the invention is to provide a drive arrangement for a discharge spout which includes an overload clutch that automatically reestablishes the driving connection between the drive motor and the discharge spout as soon as the excessive torque acting upon the discharge spout is reduced. In normal operation the overload clutch transmits the driving torque from the drive motor to the discharge spout. Thus, the overload clutch separates the driveline, that connects the drive motor with the discharge spout so as to transmit normal torque, in the event the torque to be transmitted exceeds a threshold value, as may be caused by the discharge spout striking an obstacle during the operation, resulting in the discharge spout transmitting a torque to the drive motor, or as may be caused by the drive motor forcing the discharge spout against a fixed obstacle resulting in an applied load exceeding the normal torque. When the discharge spout no longer interacts with the obstacle the overload clutch again engages automatically, so that normal operation is again possible. Appropriate overload clutches are, for example, cam controlled clutches and star ratchets.
In this way damage to the discharge spout is avoided by simple means and after an impact with an obstacle normal operation is again immediately possible.
Yet another object of the invention is to provide a drive for a discharge spout that includes a clutch that is operable for providing a braking force that acts to prevent the discharge spout from swinging freely after an impact with an obstacle. An example of an overload clutch which is operable to provide a braking torque after it has interrupted the driveline is a friction clutch.